Grafted para-aramid fiber and method of making

ABSTRACT

A fiber comprising poly(p-phenylene terephthalamide) having monomers such as N-(4-vinylphenyl)maleimide grafted onto the fiber surface.

BACKGROUND

1. Field of the Invention

This invention pertains to the field of grafted aromatic polyamide orcopolyamide fibers.

2. Description of Related Art

U.S. Pat. Nos. 6,045,907 and 6,358,451 to Rebouillat disclosepoly(p-phenylene terephthalamide) fibers that have been grafted withnitrobenzyl, allyl, or nitrostilbene groups to increase adhesion of thefibers to rubber. A process for making the grafted fibers that requireswet or never-dried as-spun para-aramid fibers to prepare thebase-activated fibers for the grafting step is also disclosed.References are cited therein that disclose alternative processes forpreparing grafted fibers to improve their adhesion with a variety ofpolymeric matrices.

There is an ongoing need to provide para-aramid type fibers that haveenhanced adhesion for reinforcement of polymeric matrices.

SUMMARY OF THE INVENTION

This invention pertains to a fiber comprising poly(p-phenyleneterephthalamide) having monomers such as N-(4-vinylphenyl)maleimidegrafted onto the fiber surface.

The invention further pertains to a method of making a fiber comprisingpoly(p-phenylene terephthalamide) having monomers such asN-(4-vinylphenyl)maleimide grafted onto the fiber surface. In addition,the invention pertains to the use of grafted fibers for thereinforcement of composites and mechanical rubber goods.

DETAILED DESCRIPTION Fiber

The fiber is an aromatic polyamide or copolyamide fiber. A preferredaromatic polyamide is para-aramid by virtue of having exceptionaltensile strength and modulus. As used herein, the term para-aramidfilaments means filaments made of para-aramid polymer. The term aramidmeans a polyamide wherein at least 85% of the amide (—CONH—) linkagesare attached directly to two aromatic rings. Suitable para-aramid fibersand their properties are described in Man-Made Fibres—Science andTechnology, Volume 2, in the section titled Fibre-Forming AromaticPolyamides, page 297, W. Black et al., Interscience Publishers, 1968.Aramid fibers and their production are, also, disclosed in U.S. Pat.Nos. 3,767,756; 4,172,938; 3,869,429; 3,869,430; 3,819,587; 3,673,143;3,354,127; and 3,094,511.

A preferred para-aramid is poly(p-phenylene terephthalamide), which iscalled PPD-T. By PPD-T is meant the homopolymer resulting frommole-for-mole polymerization of p-phenylene diamine and terephthaloylchloride and, also, copolymers resulting from incorporation of smallamounts of other diamines with the p-phenylene diamine and of smallamounts of other diacid chlorides with the terephthaloyl chloride. As ageneral rule, other diamines and other diacid chlorides can be used inamounts up to as much as about 10 mole percent of the p-phenylenediamine or the terephthaloyl chloride, or perhaps slightly higher,provided only that the other diamines and diacid chlorides have noreactive groups that interfere with the polymerization reaction. PPD-T,also, means copolymers resulting from incorporation of other aromaticdiamines and other aromatic diacid chlorides such as, for example,2,6-naphthaloyl chloride or chloro- or dichloroterephthaloyl chloride or3,4′-diaminodiphenylether. Additives can be used with the aramid and ithas been found that up to as much as 10 percent or more, by weight, ofother polymeric material can be blended with the aramid. Copolymers canbe used having as much as 10 percent or more of other diaminesubstituted for the diamine of the aramid or as much as 10 percent ormore of other diacid chloride substituted for the diacid chloride of thearamid.

Another suitable fiber is one based on aromatic copolyamide such as isprepared by reaction of terephthaloyl chloride (TPA) with a 50/50 moleratio of p-phenylene diamine (PPD) and 3,4′-diaminodiphenyl ether (DPE).Yet another suitable fiber is that formed by polycondensation reactionof two diamines, p-phenylene diamine and5-amino-2-(p-aminophenyl)benzimidazole with terephthalic acid oranhydrides or acid chloride derivatives of these monomers.

In some embodiments, the fiber is in the form of a continuous filament.For purposes herein, the term “filament” is defined as a relativelyflexible, macroscopically homogeneous body having a high ratio of lengthto width across its cross-sectional area perpendicular to its length.The filament cross section can be any shape, but is typically round orbean shaped. Multifilament yarn spun onto a bobbin in a package containsa plurality of continuous filaments. In the context of this disclosure,the terms filament and fiber may be used interchangeably.

In some other embodiments, the fiber is in the form of a pulp. Pulp is afibrillated fiber product that is manufactured from yarn by choppinginto staple then mechanically abrading in water to partially shatter thefibers. This leads to a large increase in surface area as fibrils withdiameters as low as 0.1 μm are attached to the surface of the mainfibers, which are typically 12 μm in diameter. Such pulps must be keptmoist to prevent the fibrillar morphology from collapsing if they are tobe highly dispersible in different matrices. The pulps are used asfillers in elastomer compounds to modify their tensile properties. Thelargest application is in natural rubber for mechanical rubber goodssuch as in tire reinforcement. The moist pulps are dispersed into waterand mixed with elastomer latexes then coagulated to give concentratedmasterbatches. An exemplary masterbatch is known as Kevlar® EngineeredElastomer (EE) available from E.I. DuPont de Nemours and Company,Wilmington, Del. The EE masterbatches contain the pulp in a highlydispersed state that can be compounded into bulk elastomer to give thedesired level of pulp modification.

Other suitable forms of fibrous material are a staple spun yarn, anonwoven fabric, floc or chopped yarn strand. A plurality of filamentsor yarns may be combined to form a cord. These terms are well known inthe textile fibers art.

Grafting onto Fiber

The para-aramid fibers described above have amide linkages exposed onthe fiber surface that can be used as reaction sites for grafting ofmonomers. Such grafting reactions in the prior art have required thecombination of dipolar aprotic solvents, particularly dimethylsulfoxide,with strong bases, such as potassium tert-butoxide and sodium hydride,to generate anions at the amide sites. However, these conditions arealso capable of dissolving the resulting anionic aramid polymer off ofthe fiber surface and degrading the fiber properties in an undesirablemanner. The methods disclosed herein avoid these problems and cancleanly graft a wide variety of monomers onto the fiber surface. Themonomers are chosen to improve adhesion of the grafted fibers with avariety polymeric matrices and thereby enhance the reinforcement oftheir fiber-reinforced articles. Suitable monomers are an allyl halide,a substituted benzyl chloride, a substituted N-phenylmaleimide or asubstituted epoxy. Preferably, such monomers will contain at least tworeactive functional groups, the first being capable of undergoing thegrafting reaction and the second being capable of reacting with thepolymeric matrix. The base monomer group typically undergoes thegrafting reaction while the substituted group preferably is a functionalgroup that is capable of reacting with the polymeric matrix, such as anallyl, vinyl, or epoxy group. More specifically, the substituted benzylchloride is 4-vinylbenzyl chloride or 3-vinylbenzyl chloride, thesubstituted N-phenymaleimide is N-(4-vinylphenyl)maleimide, and thesubstituted epoxy is 4,4′-methylene-bis(N,N-diglycidylaniline),epichlorohydrin, or epibromohydrin.

The majority of these monomers graft as a single monomeric group ontothe amide sites on the fiber surface, which limits the achievable graftlevel in terms of weight-precent grafted monomer. An exception to thistrend is the substituted N-phenymaleimide monomers, which undergo agraft polymerization reaction of the maleimide groups that is intiatedby the anionic amide site on the fiber surface. The principles ofanionic polymerization of N-substituted maleimide monomers are discussedin an article by T. Hagiwara et al., Macromolecules, volume 24, pages6856-6858 (1991). In particular, substituted N-phenylmaleimide monomersare preferred because their polymerizations exhibit “living”characteristics for better control of polymer molecular weight andstructure. Graft polymerization of a substituted N-phenylmaleimidemonomer leads to higher weight-percent graft levels than is possiblewith the grafting of monomeric groups. If the substitutedN-phenylmaleimide monomer is N-(4-vinylphenyl)maleimide, graftpolymerization leads to more than one vinyl group being grafted to thefiber surface thereby increasing the potential for enhanced adhesionbetween the grafted fiber and a polymeric matrix.

In some embodiments, the grafted fiber comprises poly(p-phenyleneterephthalamide) having N-(4-vinylphenyl)maleimide groups grafted ontothe fiber surface. Preferably, the N-(4-vinylphenyl)maleimide groupscomprise 0.1 to 10 weight % of the total weight of the fiber. Morepreferably, the N-(4-vinylphenyl)maleimide groups comprise 1 to 10weight % of the total weight of the fiber.

In some embodiments, the hydrogen on 0.25 to 75 mole percent of theamide sites of the poly(p-phenylene terephthalamide) on the fibersurface has been replaced by grafting N-(4-vinylphenyl)maleimide groups.More preferably, the hydrogen on 10 to 50 mole percent of the amidesites on the fiber surface have been replaced by graftingN-(4-vinylphenyl)maleimide groups.

Method of Making Grafted Fiber

A method of making a fiber comprised of poly(p-phenyleneterephthalamide) having monomer groups grafted onto the fiber surface,the method comprising the steps of:

-   -   (i) providing a fiber of poly(p-phenylene terephthalamide) that        has been dried to remove adsorbed moisture,    -   (ii) treating the fiber, in a non-polar solvent that will not        dissolve the fiber, with a phosphazene base that exhibits a pKa        in dimethylsulfoxide of at least 21 so as to generate anions at        the amide sites on the surface of the poly(p-phenylene        terephthalamide) fiber, and    -   (iii) grafting a monomer onto the anion sites so as to introduce        reactive functional groups onto the surface of the        poly(p-phenylene terephthalamide) fiber.

Further optional steps such as washing and drying the grafted fiber maybe carried out. This method of using a combination of a non-polarsolvent with a phosphazene base to generate the anionic amide sites iseffective at grafting the monomers to the fiber surface withoutdegrading the exceptional physical properties of para-aramid fibers.

In a preferred embodiment, the phosphazene base exhibits a pKa indimethylsulfoxide of at least 30. Suitable non-polar solvents areaprotic and include linear or alicyclic hydrocarbons, aromatichydrocarbons, or ethers. Preferably, the non-polar solvent is toluene ortetrahydrofuran.

Preferably, the phosphazene base is an iminophosphorane,phosphazophosphazene, aminophosphazene, guanidinophosphazene, orphosphatrane. Examples of such phosphazene bases and their chemicalproperties are described by Kolomeitsev et al. in the Journal of theAmerican Chemical Society, volume 127, pages 17656-17666 (2005). Suchphosphazene bases display high basicity even in non-polar solvents andlow nucleophilicity compared to typical strong bases used in the priorart on para-aramid fibers. More preferably, the phosphazene base is thetertiary-butyl-P₄-phosphazene. Preferably the grafting base solution hasa grafting agent concentration of 0.0005 to 6 molar. A suitable monomeris an allyl halide, a substituted benzyl chloride, a substitutedN-phenylmaleimide or a substituted epoxy. Preferably, wherein thesubstituted benzyl chloride is 4-vinylbenzyl chloride or 3-vinylbenzylchloride, the substituted N-phenymaleimide isN-(4-vinylphenyl)maleimide, and the substituted epoxy is4,4′-methylene-bis(N,N-diglycidylaniline), epichlorohydrin, orepibromohydrin.

In a further embodiment, a method of making a fiber comprised ofpoly(p-phenylene terephthalamide) having monomer groups grafted onto thefiber surface, the method comprising the steps of:

-   -   (i) providing a fiber of poly(p-phenylene terephthalamide) that        has been dried to remove adsorbed moisture,    -   (ii) treating the fiber, in a non-polar solvent that will not        dissolve the fiber, with a phosphazene base that exhibits a pKa        in dimethylsulfoxide of at least 21 so as to generate anions at        the amide sites on the surface of the poly(p-phenylene        terephthalamide) fiber,    -   (iii) grafting a monomer onto the anion sites so as to introduce        reactive functional groups onto the surface of the        poly(p-phenylene terephthalamide) fiber, and    -   (iv) washing the grafted fiber of step (iii) with a protic        solvent to extract any residual base compounds and grafting        agents that are unbound to the surface of the fibers.

In yet another embodiment, a method of making a fiber comprised ofpoly(p-phenylene terephthalamide) having monomer groups grafted onto thefiber surface, the method comprising the steps of:

-   -   (i) providing a fiber of poly(p-phenylene terephthalamide) that        has been dried to remove adsorbed moisture,    -   (ii) treating the fiber, in a non-polar solvent that will not        dissolve the fiber, with a phosphazene base that exhibits a pKa        in dimethylsulfoxide of at least 21 so as to generate anions at        the amide sites on the surface of the poly(p-phenylene        terephthalamide) fiber,    -   (iii) washing the base-activated fiber with a non-polar solvent        to eliminate excess base compounds,    -   (iv) grafting a monomer onto the anion sites so as to introduce        reactive functional groups onto the surface of the        poly(p-phenylene terephthalamide) fiber, and    -   (v) washing the grafted fiber of step (iv) with a protic solvent        to extract any residual base compounds and grafting agents that        are unbound to the surface of the fibers.

Suitable protic solvents for washing of the grafted fiber includealcohols, glycols, carboxylic acids, water, and their mixtures.Preferably, the protic solvent is methanol or water.

Embodiments similar to those described above are applicable to fiber inthe form of filament, continuous filament yarn, cord, spun staple yarn,nonwoven fabric, floc, pulp or chopped strand. Whereas pulps aretypically kept moist, they must be carefully dried for the graftingmethods described above to preserve their ability to be highlydispersible in different polymeric matrices and concentratedmasterbatches. The preferred method for the drying of moist or evenhighly hydrated pulps is to freeze-dry them as disclosed in U.S. patentapplication Ser. No. 13/551,674 filed Jul. 18, 2012.

Composite

Fibers comprising poly(p-phenylene terephthalamide) having monomers suchas N-(4-vinylphenyl)maleimide groups grafted onto the fiber surface maybe combined with a matrix resin to form a fiber-reinforced resincomposite. Suitable fiber forms include a continuous filament yarn, spunstaple yarn, nonwoven fabric, pulp or chopped strand. The resin may be athermoset or thermoplastic resin. Typically the matrix resin comprisesfrom 30 to 50 weight percent of the weight of fiber plus resin in thecomposite. Suitable thermoset resins include epoxy, phenolic,epoxy-novolac, cyanate ester, unsaturated ester, melamine and maleimide.The fibers may be treated by any of the methods described above. In asimilar way, monomers other than N-(4-vinylphenyl)maleimide may begrafted onto the surface of poly(p-phenylene terephthalamide) fiberprior to combining the fiber with a matrix resin to form afiber-reinforced resin composite. Other suitable momoners include anallyl halide, a substituted benzyl chloride, a substitutedN-phenylmaleimide or a substituted epoxy that are grafted to the fiberusing the methods described herein. Preferably, wherein the substitutedbenzyl chloride is 4-vinylbenzyl chloride or 3-vinylbenzyl chloride, thesubstituted N-phenymaleimide is N-(4-vinylphenyl)maleimide, and thesubstituted epoxy is 4,4′-methylene-bis(N,N-diglycidylaniline),epichlorohydrin, or epibromohydrin.

Mechanical Rubber Goods

Fibers comprising poly(p-phenylene terephthalamide) having monomers suchas N-(4-vinylphenyl)maleimide groups grafted onto the fiber surface maybe combined with an elastomer to form a fiber-reinforced rubber article.Suitable fiber forms include a continuous filament yarn, spun stapleyarn, nonwoven fabric, pulp or chopped strand. Suitable elastomersinclude both natural rubber, synthetic natural rubber and syntheticrubber. Synthetic rubber compounds can be any that are dissolved bycommon organic solvents and can include, among many others,polychloroprene and sulfur-modified chloroprene, hydrocarbon rubbers,butadiene-acrylonitrile copolymers, styrene butadiene rubbers,chlorosulfonated polyethylene, fluoroelastomers, polybutadiene rubbers,polyisoprene rubbers, butyl and halobutyl rubbers and the like. Naturalrubber, styrene butadiene rubber, polyisoprene rubber and polybutadienerubber are preferred. Mixtures of rubbers may also be utilized. In oneembodiment, a dipped cord suitable for use in a rubber compoundcomprises fiber comprising poly(p-phenylene terephthalamide) havingmonomers such as N-(4-vinylphenyl)maleimide groups grafted onto thefiber surface coated with a styrene-butadiene-vinylpyridine rubberlatex. Carbon black and silica may optionally be present in thestyrene-butadiene-vinylpyridine rubber latex used to coat the graftedcord. The fibers may be treated by any of the methods described above.In a similar way, monomers other than N-(4-vinylphenyl)maleimide may begrafted onto the surface of poly(p-phenylene terephthalamide) fiberprior to combining the fiber with an elastomer to form afiber-reinforced elastomeric compound. Other suitable monomers includean allyl halide, a substituted benzyl chloride, a substitutedN-phenylmaleimide or a substituted epoxy that are grafted to the fiberusing the methods described herein. Preferably, wherein the substitutedbenzyl chloride is 4-vinylbenzyl chloride or 3-vinylbenzyl chloride, thesubstituted N-phenymaleimide is N-(4-vinylphenyl)maleimide, and thesubstituted epoxy is 4,4′-methylene-bis(N,N-diglycidylaniline),epichlorohydrin, or epibromohydrin.

TEST METHODS

The H-pull adhesion measurements were performed according to ASTMD4776-10 using an extensometer. The H-pull samples were molded using astandard rubber stock as described by Y. Iyengar, J. Appl. Polym. Sci.,1978, 22, 801-812. The adhesion values are reported in units ofpounds-force (lbf) as the average of at least five samples.

The specific surface areas were measured by nitrogenadsorption/desorption at liquid nitrogen temperature (77.3 K) using aMicromeritics ASAP 2405 porosimeter. Samples were out-gassed overnightat a temperature of 150° C., unless noted otherwise, prior to themeasurements and the weight losses were determined due to adsorbedmoisture. A five-point nitrogen adsorption isotherm was collected over arange of relative pressures, P/P₀, from 0.05 to 0.20 and analyzedaccording to the BET method (S. Brunauer, P. H. Emmett, and E. Teller,J. Am. Chem. Soc. 1938, 60, 309); P is the equilibrium gas pressureabove the sample, P₀ is the saturation gas pressure of the sample,typically greater than 760 Torr.

The tensile stress-strain measurements were performed according to ASTMD412-06a, method A, using an extensometer. Dumbell tensile bars were cutusing Die C as described in Method A. The tensile results are reportedas the average of six samples.

EXAMPLES

Abbreviations used in the examples and tables are as follows: mL(milliliter), mmole (millimole), wt (weight), THF (tetrahydrofuran), ECP(epichlorohydrin), VBC (4-vinylbenzyl chloride), VPM(N-(4-vinylphenyl)maleimide), MBDGA (4,4′-methylenebis(N,N-diglycidylaniline)), AS (4-aminostyrene), EMI-24(2-ethyl-4-methylimidazole), TGA (thermal gravimetric analysis), ATR IR(attenuated total reflectance infrared spectroscopy), VPL (vinylpyridinelatex), RFL (resorcinol-formaldehyde-vinylpyridine latex), BET(Brunauer-Emmett-Teller specific surface area), T (temperature), MD(machine direction), XD (cross-machine direction), phr (parts perhundred rubber).

Unless noted, the examples were prepared using materials supplied by theAldrich Chemical Company, Milwaukee, Wis., including P₁tBu phosphazene,P_(i)tBu[(CH₂)₄]₃ phosphazene, P₂tBu phosphazene in THF solution (2M),P₄tBu phosphazene in hexane solution (1M), and 4-vinylbenzyl chloride(90% technical grade); GenTac® FS vinylpyridine latex(vinylpyridine-butadiene-styrene terpolymer emulsion, 41% total solidsin water), Omnova Solutions Inc.; Alcogum® 6940 thickener (polyacrylicacid, sodium salt; 11% solids) and Alcogum® SL 70 dispersing agent(acrylate copolymer; 30% solids), Akzo Nobel Surface Chemistry,Chattanooga, Tenn.; Aquamix™ 125 (Wingstay® L, hindered polymericphenolic antioxidant, 50% solids) and Aquamix™ 549 (zinc2-mercaptotoluimidazole, 50% solids) dispersions, PolyOne Corp.,Massillon, Ohio; Amax® OBTS accelerator(N-oxydiethylene-2-benzothiazole-sulfenamide) and AgeRite® Resin Dantioxidant (polymerized 1,2-dihydro-2,2,4-trimethylquinoline), R. T.Vanderbilt Co., Norwalk, Conn.; DPG accelerator (diphenyl guanidine),Akrochem Corp., Akron, Ohio; Santoflex® 6PPD antiozonant(N-(1,3-dimethylbutyI)-N′-phenyl-para-phenylenediamine),Solutia/Flexsys® America, Akron, Ohio. N-(4-vinylphenyl)maleimide wassupplied by Acros Organics or prepared according to T. Hagiwara et al.,Macromolecules, volume 24, pages 6856-6858 (1991). Kevlar® 29 cord(finish-free, 2 plies of 1500 denier yarn), RFL-coated Kevlar® 29 cord,and Kevlar® pulp 1 F361 (BET 7-9 m²/g) were obtained from E. I. Du Pontde Nemours and Company, Wilmington, Del. The reactions were run undernitrogen using glassware dried at 120° C.

The following examples are given to illustrate the invention and shouldnot be interpreted as limiting it in any way. All parts and percentagesare by weight unless otherwise indicated. Examples prepared according tothe process or processes of the current invention are indicated bynumerical values. Control or Comparative Examples are indicated byletters. Data and test results relating to the Comparative and InventiveExamples are summarized in Tables 1 to 6.

Example 1

Kevlar® 29 cord was cut into 1.5 inch lengths that were placedindividually into glass vials and dried overnight at 80° C. undervacuum. The vials were transferred to a nitrogen-purged glove box. Thecord samples were covered with a variety of anhydrous solvents (5 mL)and treated with various phosphazene bases (10 drops) while examiningfor any visual changes. The cords were then allowed to sit overnight.Table 1 summarizes the observed visual changes along with the pK valuesreported in the literature for the phosphazene bases. These results showthat the P₄tBu phosphazene has high enough pK values to generate thepolyanion on the fiber surface without dissolving it in a non-polarsolvent like toluene or THF. P₂tBu phosphazene has high enough pK valuesto generate the polyanion and dissolve it in DMSO.

TABLE 1 Phos- phazene P₁tBu P₁tBu[(CH₂)₄]₃ P₂tBu/THF P₄tBu/HexanepK_(BH) + 26.9 28.4 33.5 41.9 (CH₃CN) pK_(a) ~15 ~16 21 30 (DMSO) Hexanenone none none darker yellow cord, clear solution Cyclo- none none nonedarker yellow cord, hexane clear solution Toluene none none none orangecord, clear solution THF none none yellow cord, dark orange cord, lightviolet faint yellow solution solution Pyridine none none yellow cord,orange cord, off-colored red-orange solution solution Aceto- none noneyellow cord, yellow cord nitrile yellow solution and solution DMSO nonenone dissolved cord, yellow-orange thick orange cord and solutionsolution

Example 2

Kevlar® 29 cord (3 meters) was wound onto a glass stirring rod andsecured using Teflon® tape; the cord weighed about 1 g (8.4 mmole amidegroups). The assembly was dried at 120° C. under vacuum. Inside theglove box, a solution of P₄tBu phosphazene (0.82 mL, 0.82 mmole, 9.8mole %) in anhydrous toluene (100 mL) was prepared in a 200 mL tubeequipped with a Teflon® stirring bar, two-way adapter, gas-tight Teflon®stirrer bearing, and gas inlet. The cord was immersed in the phosphazenesolution to give an immediate color change and heated to 30° C. After 45minutes, the cord was rust-orange in color and the solution wascolorless. After 2 hours, there was essentially no change, so the cordwas transferred to a solution of epichlorohydrin (0.66 mL, 8.4 mmole,100 mole %) in anhydrous toluene (100 mL) in a 200 mL tube while keepingblanketed under nitrogen. After 1 hour at 25° C., the orange color hadfaded some, and after stirring overnight, the color had faded almostcompletely back to yellow. The cord was washed by soaking several timesin fresh toluene. Samples of the cord were dried under vacuum foranalysis. TGA showed a weight loss of 1.6 wt % between 200 and 400° C.due to the grafted groups. ATR IR showed increased absorbances at2800-3000 cm⁻¹ for C—H bonds relative to untreated cord. The H-pulladhesion was 6.8 lbf relative to 5.2 lbf for untreated cord.

Example 3

The procedure of Example 2 was repeated using less P₄tBu phosphazene(0.21 mL, 2.5 mole %) and 4-vinylbenzyl chloride (0.14 g, 0.84 mmole, 10mole %) for the grafting reaction. After 20 minutes of grafting, therust-orange color had faded to yellow and after 1 hour to light yellow.After stirring overnight, the cord was worked up and analyzed as before.TGA showed a weight loss of 0.7 wt % between 200 and 400° C. due to thegrafted 4-vinylbenzyl groups. The H-pull adhesion was 9.6 lbf.

Example 4

The procedure of Example 3 was repeated using more P₄tBu phosphazene(0.42 mL, 5 mole %) and 4-vinylbenzyl chloride (1.1 g, 7 mmole, 83 mole%). After 5 minutes of grafting, the color had faded to yellow-orangeand after 2 hours to light yellow. After stirring overnight, the cordwas quenched by soaking in methanol and washed twice each with methanoland toluene. TGA showed a weight loss of 0.1 wt % between 200 and 400°C. due to the grafted 4-vinylbenzyl groups. The H-pull adhesion was 10.6lbf.

Example 5

The procedure of Example 4 was repeated using more P₄tBu phosphazene(0.84 mL, 10 mole %) and anhydrous THF as the solvent. After 5 minutesof grafting, the color had faded to yellow-orange and after overnight tolight yellow. TGA showed a weight loss of 0.9 wt % between 150 and 400°C. due to the grafted 4-vinylbenzyl groups. The H-pull adhesion was 10.1lbf.

Example 6

The procedure of Example 5 was repeated using 4,4′-methylenebis(N,N-diglycidylaniline) (3 g, 7 mmole) for the grafting reaction.After 30 minutes of grafting, the color had faded slightly and afterovernight to yellow-orange. TGA showed a weight loss of 1.8 wt % between200 and 400° C. due to the grafted epoxy groups. ATR IR showed increasedabsorbances at 3500 cm⁻¹ for hydroxyl groups, 2800-3000 cm⁻¹ for C—Hbonds, and 1510 cm⁻¹ for aromatic groups relative to untreated cord. TheH-pull adhesion was 7.2 lbf.

to Example 7

Kevlar® 29 cord (3 meters) was wound onto a glass stirring rod andsecured using Teflon® tape; the cord weighed about 1 g (8.4 mmole amidegroups). The assembly was dried at 120° C. under vacuum then transferredto the glove box. Inside the glove box, a solution of P₄tBu phosphazene(1.7 mL, 1.7 mmole, 20 mole %) in anhydrous THF (100 mL) was prepared ina 200 mL tube equipped with a Teflon® stirring bar, two-way adapter,Teflon® stirrer adapter, and gas inlet. The cord was immersed in thephosphazene solution to give an immediate color change. After 15 minutesat room temperature, the cord was rust-orange in color and the solutionwas clear. After about 2 hours, VBC (1.0 mL, 7 mmole) was added directlyto the tube containing the cord immersed in the phosphazene solution.The color quickly faded to orange, and after stirring overnight, thecolor had faded to yellow. The cord was quenched and washed by soakingtwice each in methanol and THF then stored under toluene. Samples of thecord were dried under vacuum for analysis. TGA showed a weight loss of1.2 wt % between 270 and 470° C. due to the grafted 4-vinylbenzylgroups. ATR IR showed increased absorbances at 2800-3000 cm⁻¹ for C—Hbonds and 1510 cm⁻¹ for aromatic groups relative to untreated cord. TheH-pull adhesion was 10.8 lbf.

Example 8

The procedure of Example 7 was repeated using VBC that had been vacuumdistilled at 65-70° C. and 1 Torr. TGA showed a weight loss of 2.2 wt %between 150 and 400° C. due to the grafted 4-vinylbenzyl groups. TheH-pull adhesion was 11.7 lbf.

Example 9

The procedure of Example 8 was repeated, except that thephosphazene-treated cord was transferred to a fresh solution of VBC inTHF (100 mL). TGA showed a weight loss of 0.5 wt % between 170 and 400°C. due to the grafted 4-vinylbenzyl groups. ATR IR showed increasedabsorbances at 1510 cm⁻¹ for aromatic groups relative to untreated cord.The H-pull adhesion was 9.8 lbf.

Example 10

The procedure of Example 8 was repeated using less P₄tBu phosphazene(0.8 mL, 10 mole %). TGA showed a weight loss of 0.3 wt % between 200and 400° C. due to the grafted 4-vinylbenzyl groups. The H-pull adhesionwas 10.7 lbf.

is Example 11

The procedure of Example 9 was repeated using less P₄tBu phosphazene(0.8 mL, 10 mole %) and N-(4-vinylphenyl)maleimide (1 g, 5 mmole, 60mole %) for the grafting reaction. After the overnight graftingreaction, the grafted cord was still rust-orange in color. The cordretained some color after quenching and washing in methanol. TGA showeda weight loss of 4.3 wt % between 200 and 520° C. due to the graftpolymerization of the maleimide groups. ATR IR showed increasedabsorbances at 2800-3200 cm⁻¹ for C—H bonds, intense absorbances at1701, 1512, 1392, and 1182 cm⁻¹ for the imide and aromatic groups, andabsorbances at 987 and 910 cm⁻¹ for the vinyl groups relative tountreated cord. The H-pull adhesion was 13.3 lbf.

Example 12

The procedure of Example 11 was repeated using less P₄tBu phosphazene(0.4 mL, 5 mole %). After the overnight grafting reaction, the graftedcord was still dark orange in color so the reaction was continued at 40°C. for 2 hours then at 60° C. for 2 hours. The cord retained some colorafter quenching and washing in methanol. TGA showed a weight loss of 6.3wt % between 400 and 530° C. due to the graft polymerization of themaleimide groups. ATR IR showed increased absorbances at 2800-3000 cm⁻¹for C—H bonds, intense absorbances at 1701, 1512, 1390, and 1182 cm⁻¹for the imide and aromatic groups, and absorbances at 985 and 910 cm⁻¹for the vinyl groups relative to untreated cord. The H-pull adhesion was12.9 lbf.

Example 13

The procedure of Example 11 was repeated using 4,4’-methylenebis(N,N-diglycidylaniline) for the grafting reaction. TGA showed aweight loss of 3.4 wt % between 200 and 500° C. due to the graftpolymerization of the epoxy groups. ATR IR showed decreased absorbancesat 3200 cm⁻¹ for amide groups and increased absorbances at 2800-3000cm⁻¹ for C—H bonds and at 1512 cm⁻¹ for aromatic groups relative tountreated cord. The H-pull adhesion was 6.6 lbf.

Example 14

The procedure of Example 13 was repeated, except that the P₄tBuphosphazene treatment was continued overnight before treating with4,4′-methylene bis(N,N-diglycidylaniline) for the grafting reaction. TGAshowed a weight loss of 6.4 wt % between 200 and 500° C. due to thegraft polymerization of the epoxy groups. ATR IR showed decreasedabsorbances at 3200 cm⁻¹ for amide groups and increased absorbances at3500 cm⁻¹ for hydroxyl groups, at 2800-3000 cm⁻¹ for C—H bonds, and at1512 cm⁻¹ for aromatic groups relative to untreated cord. The H-pulladhesion was 7.1 lbf.

Comparative Example A

The H-pull adhesion for an untreated sample of Kevlar® 29 cord was 5.2lbf.

Comparative Example B

The procedure of Example 14 was repeated without using any monomer forthe grafting reaction. TGA showed a weight loss of 1.5 wt % between 150and 400° C. The H-pull adhesion was 5.8 lbf

Comparative Example C

The procedure of Example 7 was repeated using potassium tert-butoxide(0.2 g, 1.8 mmole, 21 mole %) instead of the P₄tBu phosphazene and cordwas treated overnight before adding the VBC for the grafting reaction.TGA showed a weight loss of 0.4 wt % between 200 and 450° C. The H-pulladhesion was 6.3 lbf.

Comparative Example D

Kevlar® 29 cord (4.5 meters) was wound onto a glass stirring rod andsecured using Teflon® tape; the cord weighed about 1.5 g (12.6 mmoleamide groups). The assembly was dried at 80° C. under vacuum. A solutionof methyl sulfinyl anion in anhydrous DMSO (100 mL) was prepared in a200 mL tube equipped with a Teflon® stirring bar, two-way adapter,gas-tight Teflon® stirrer bearing, and gas inlet by adding sodiumhydride (0.15 g, 6.25 mmole, 50 mole %) to the tube, heating undernitrogen to 70° C. until the solids completely dissolved, and cooling toroom temperature. The cord was immersed in the solution to immediatelygive a slight color change. After 15 minutes, the cord was lightyellow-orange in color. After 1 hour, the cord was medium orange incolor and the solution was pale yellow. The cord was transferred to asolution of 4-vinylbenzyl chloride (1 mL, 7.1 mmole, 56 mole %) inanhydrous THF (100 mL) in a 200 mL tube while keeping blanketed undernitrogen. After 1 hour at 25° C., the color was unchanged. After 3hours, there was only a slight fading of the orange color. Afterstirring overnight, the color had not faded further. The cord was washedby soaking several times in fresh methanol to return it to its originalyellow color and stored under toluene. Samples of the cord were driedunder vacuum for analysis. TGA showed a weight loss of 1.3 wt % between300 and 500 ° C. due to the grafted groups. ATR IR showed increasedabsorbances at 2800-3200 cm−1 for C—H bonds, at 1510 cm−1 for aromaticgroups, and absorbances at 980 and 910 cm−1 for the vinyl groupsrelative to untreated cord. The H-pull adhesion was 9.0 lbf.

The Inventive Examples 2-14 and Comparative Examples A-D are summarizedwith their results in Table 2.

TABLE 2 P₄tBu Monomer TGA H-Pull Example Solvent mole % mole % wt % lbf2 toluene   9.8 ECP 100  1.6 6.8 3 toluene   2.5 VBC 10 0.7 9.6 4toluene  5 VBC 83 0.1 10.6 5 THF 10 VBC 83 0.9 10.1 6 THF 10 MBDGA 831.8 7.2 7 THF 20 VBC 83 1.2 10.8 8 THF 20 VBC^(a) 83 2.2 11.7 9 THF 20VBC^(a) 83 0.5 9.8 10 THF 10 VBC^(a) 83 0.3 10.7 11 THF 10 VPM 60 4.313.3 12 THF  5 VPM 60 6.3 12.9 13 THF 10 MBDGA 83 3.4 6.6 14 THF 10MBDGA 83 6.4 7.1 A — — — — — 5.2 B THF 10 none — 1.5 5.8 C THF  21^(b)VBC 83 0.4 6.3 D DMSO  50^(c) VBC 56 1.3 9.0 ^(a)distilled.^(b)potassium tert-butoxide. ^(c)sodium hydride.

Examples 15-21, Comparative Examples E-G

The grafted cords of Examples 8, 10, 11, and 12, and ComparativeExamples B, C and D were treated by dipping into vinylpyridine latexdiluted to various percent solids and suspending parallel to the benchtop to air dry. Several samples were dipped a second time. The TGAresults and H-pull adhesion values are shown in Table 3.

Comparative Examples H and I

Kevlar® 29 cords that are coated with a standard RFL formulation asdescribed by Y. Iyengar, J. Appl. Polym. Sci., 1978, 22, 801-812typically give H-pull adhesion values of about 30 lbf. Several batchesof RFL-coated cord and standard rubber stock were tested to confirmthese values as shown in Table 3.

TABLE 3 Cord Cord VPL TGA H-Pull Example Example Treatment wt % dips wt% lbf 15 8 VBC 15 1  8.6 21.3 16 8 VBC 15 2 15.3 31.3 17 10 VBC 25 117.5 39.6 18 11 VPM 15 1 15.5 28.9 19 11 VPM 15 2 22.2 26.1 20 12 VPM 151 14.7 26.6 21 12 VPM 15 2 20.2 29.5 E B none 15 1 15.3 10.3 F C VBC 251 14.7 13.0 G D VBC 25 1 17.9 21.5 H — RFL — — — 28.9 I — RFL — — — 34.5

Examples 22-26

Samples of the MBDGA-grafted cord from Example 13 were treated withsolutions of either 0.3% 2-ethyl-4-methylimidazole in methanol, 6%4-aminostyrene in 2-butanone containing 0.3% 2-ethyl-4-methylimidazole,or 20% 4-aminostyrene in 2-butanone. Some of the treated cords were thendipped in vinylpyridine latex diluted to 25% solids. The cords weresuspended parallel to the bench top to air dry after each treatment. TheTGA results and H-pull adhesion values are shown in Table 4.

TABLE 4 Cord Solution VPL TGA H-Pull Example Treatment wt % (25 wt %) wt% lbf 22 EMI-24   0.3 yes 24.6 13.3 23 AS/EMI-24 6/0.3 no 7.4 11.6 24AS/EMI-24 6/0.3 yes 22.1 16.8 25 AS 20 no 7.3 10.4 26 AS 20 yes 23.517.0

Examples 27-33

Samples of the MBDGA-grafted cord of Example 14 were treated withsolutions of either 10% 4-aminostyrene in water containing 10% ethanoland 0.5% 2-ethyl-4-methylimidazole or 20% 4-aminostyrene in watercontaining 20% ethanol and 1% 2-ethyl-4-methylimidazole. The treatedcords were further heat-treated at 130° C. for 5 minutes and/or dippedin vinylpyridine latex diluted to 25% solids. The cords were suspendedparallel to the bench top to air dry after each treatment. The TGAresults and H-pull adhesion values are shown in Table 5.

TABLE 5 AS 130° C. VPL TGA H-Pull Example % Cure (25 wt %) wt % lbf 2710 no no 2.6 9.7 28 10 no yes 17.2 24.5 29 20 no no 3.5 9.0 30 20 no yes14.2 21.5 31 10 yes no 4.2 11.1 32 10 yes yes 24.0 17.4 33 20 yes yes26.3 13.7

Example 34

Kevlar® pulp merge 1F361 (90 g, 56% solids) was dispersed in 3.5 Ldeionized water heated to 60° C. using a high-shear mixer (IKAUltra-Turrax Model SD-45) to give a smooth slurry (1.4% solids). About2200 mL of the slurry was redispersed with the high shear mixer andvacuum filtered to give a mass of wet pulp that was then washed withdeionized water. The wet pulp was not compressed or aspirated to removeexcess moisture. The wet pulp was broken into chunks and placed in awide-mouth vacuum jar. The jar was placed in a So-Low ultra-low freezer(−40° C.) to freeze the wet pulp overnight. The jar was attached to acontinuous freeze-dryer with a dry-ice cooled trap and placed under highvacuum (30 mTorr). The jar was placed in the freezer to keep the pulpfrozen only while clearing the trap of moisture. The pulp slowly warmedto room temperature as the water finished subliming from the frozenmass. The pulp was finished by drying under high vacuum overnight togive 32 g. The specific surface area was 16.4 m²/g after a weight lossof 1.8%.

A portion of the freeze-dried Kevlar® pulp (1.5 g, 12.6 millimoles amidegroups) was placed in a 200 mL round-bottom flask equipped with a largestirring bar and dried at 120° C. in a vacuum oven. The flask wastransferred to the glove box and treated with anhydrous THF (75 mL). Thepulp was treated with a 1M solution of P₄tBu in hexane (1.3 mL, 10 mole%) to initially give it a rust-red color that faded to orange over about1 hour. 4,4′-Methylene bis(N,N-diglycidylaniline) (2.7 g, 6.4millimoles) was dissolved in THF (25 mL) and added to the pulp slurry.After stirring overnight, the slurry was diluted with THF (100 mL) andthe pulp was collected by vacuum filtration. The orange pulp wasquenched by washing twice with methanol then twice with deionized waterwhile avoiding any compaction of the filter cake. The wet pulp wasplaced in a 250 mL round bottom flask and then in the ultra-low freezer(−40° C.) to freeze the wet pulp overnight. The flask was attached to acontinuous freeze-dryer with a dry-ice cooled trap and placed under highvacuum. The pulp slowly warmed to room temperature as the water finishedsubliming from the frozen mass. The pulp was finished by drying underhigh vacuum overnight to give 1.74 g. The specific surface area was 15.4m²/g after a weight loss of 4.6%. TGA showed a weight loss of 10.1 wt %between 200 and 435° C. due to the grafted epoxy groups. ATR IR showed adecrease in the absorbance at 3300 cm⁻¹ for amide NH groups, andincreased absorbances at 2800-3000 cm⁻¹ for aliphatic groups and at 1612and 1512 cm⁻¹ for aromatic groups relative to untreated pulp.

Example 35

Freeze-dried Kevlar® pulp (1.5 g, 12.6 millimoles amide groups) with aspecific surface area of 18.4 m²/g was placed in a 200 mL round-bottomflask equipped with a large stirring bar and transferred to anitrogen-purged glove box. The pulp was treated with anhydrous THF (100mL) and stirred overnight. The solvent was decanted off and the pulp wasretreated with fresh THF. The solvent was again decanted off then thepulp was treated with sufficient THF to give about 100 mL of slurry. Thepulp was treated by stepwise addition of a 1M solution of P₄tBu inhexane (1.9 mL, 15 mole %) to initially give it a rust-red color thatfaded to dark orange over about 1 hour. The solvent was decanted off thedark-orange pulp and treated with fresh THF (100 mL). 4-Vinylbenzylchloride (0.9 mL, 6.4 millimoles) was added dropwise by pipet. Afterstirring about 2 hours, the color of the pulp had faded to a lighterorange. After stirring overnight, the color had faded to yellow. Thepulp was collected by vacuum filtration and washed with THF, methanol,and then THF. The pulp was dried under vacuum to give 1.54 g. Thespecific surface area was 3.3 m²/g after a weight loss of 3.9%. TGAshowed a weight loss of 4.0 wt % between 200 and 400° C. due to thegrafted vinylbenzyl groups. ATR IR showed a decrease in the absorbanceat 3300 cm⁻¹ for amide NH groups, and increased absorbances at 2800-3000cm⁻¹ for aliphatic groups and at 1512 cm⁻¹ for aromatic groups relativeto untreated pulp.

Example 36

Freeze-dried Kevlar® pulp (16 g, 130 millimoles amide groups) with aspecific surface area of 17.3 m²/g was placed in a 3 L three-neck Mortonflask and dried at 120° C. in a vacuum oven. The flask was equipped witha stainless steel stirring rod, gas-tight Teflon® stirrer bearing,septum, and reflux condenser with gas inlet while purging with nitrogen.Anhydrous THF (1 L) was transferred to the flask by cannula and stirredto partially disperse the pulp. Inside the glove box, a 1M solution ofP₄tBu in hexane (13 mL, 10 mole %) was added to anhydrous THF (1 L),which was then added by cannula to the Morton flask to turn the pulp alight orange color. The mixture was heated to a mild reflux during whichthe color intensified to a darker orange. After stirring for about 1hour, the orange pulp was finely dispersed in the solution and themixture was cooled to room temperature. Inside the glove box,4-vinylbenzyl chloride (9 mL, 64 millimoles) was added to anhydrous THF(100 mL), which was then added by cannula to the Morton flask. The pulpreturned to a yellow color with stirring, which was continued overnight.The solvent was removed from the flask using a glass-fritted tubeconnected to a vacuum filter flask. The pulp was washed three times withmethanol (1200 mL) then three times with deionized water (1200 mL). Aportion of the wet pulp was dried under high vacuum to determine percentsolids of 25.8%. TGA showed a weight loss of 2.6 wt % between 200 and400° C. due to the grafted vinylbenzyl groups. ATR IR showed a decreasein the absorbance at 3300 cm⁻¹ for amide NH groups relative to untreatedpulp.

Example 37

Freeze-dried Kevlar® pulp (16.2 g, 130 millimoles amide groups) with aspecific surface area of 14.3 m²/g was placed in a 3 L three-neck Mortonflask and dried at 120° C. in a vacuum oven. The flask was equipped witha stainless steel stirring rod, gas-tight Teflon® stirrer bearing,septum, and reflux condenser with gas inlet while purging with nitrogen.Anhydrous THF (1 L) was transferred to the flask by cannula and stirredto partially disperse the pulp. Inside the glove box, a 1M solution ofP₄tBu in hexane (13 mL, 10 mole %) was added to anhydrous THF (1 L),which was then added by cannula to the Morton flask. The pulp becamerust-red in color in the immediate vicinity of the added solution, butthe color faded to a light orange with stirring. The mixture was heatedto a mild reflux during which the color intensified to a darker orange.After stirring for about 3 hour, the orange pulp was finely dispersed inthe solution and the mixture was cooled to room temperature. Inside theglove box, 4-vinylbenzyl chloride (9 mL, 64 millimoles) was added toanhydrous THF (100 mL), which was then added by cannula to the Mortonflask. The pulp returned to a yellow color as it was stirred overnight.The mixture was quenched with methanol (100 mL) then the solvent wasremoved from the flask using a glass-fritted tube connected to a vacuumfilter flask. The pulp was washed three times with methanol (1200 mL)then three times with deionized water (1200 mL). A portion of the wetpulp was dried under high vacuum to determine percent solids of 27.0%.TGA showed a weight loss of 2.4 wt % between 200 and 400° C. due to thegrafted vinylbenzyl groups. ATR IR showed a decrease in the absorbanceat 3300 cm⁻¹ for amide NH groups relative to untreated pulp.

Example 38

Freeze-dried Kevlar® pulp (16 g, 130 millimoles amide groups) with aspecific surface area of 14.0 m²/g was placed in a 3 L three-neck Mortonflask and dried at 120° C. in a vacuum oven. The flask was equipped witha stainless steel stirring rod, gas-tight Teflon® stirrer bearing,septum, and reflux condenser with gas inlet while purging with nitrogen.Anhydrous THF (1 L) was transferred to the flask by cannula and stirredto partially disperse the pulp. Inside the glove box, a 1M solution ofP₄tBu in hexane (13 mL, 10 mole %) was added to anhydrous THF (1 L),which was then added by cannula to the Morton flask to turn the pulp anorange color. The mixture was heated to a mild reflux during which thecolor intensified to a darker orange. After stirring for about 2 hour,the orange pulp was finely dispersed in the solution and the mixture wascooled to room temperature. Inside the glove box, 4,4’-methylenebis(N,N-diglycidylaniline) (11 g, 26 millimoles) was dissolved inanhydrous THF (100 mL), which was then added by cannula to the Mortonflask. The orange pulp became less intense in color as it was stirredovernight. The mixture was quenched with methanol (100 mL) then vacuumfiltered to collect the yellow pulp. The pulp was washed three timeswith methanol (1200 mL) then three times with deionized water (1200 mL).A portion of the wet pulp was dried under high vacuum to determinepercent solids of 24.6%. TGA showed a weight loss of 4.0 wt % between200 and 500° C. due to the grafted epoxy groups. ATR IR showed adecrease in the absorbance at 3300 cm⁻¹ for amide NH groups relative tountreated pulp.

Example 39

Freeze-dried Kevlar® pulp (16 g, 130 millimoles amide groups) with aspecific surface area of 14.0 m²/g was placed in a 3 L three-neck Mortonflask and dried at 120° C. in a vacuum oven. The flask was equipped witha stainless steel stirring rod, gas-tight Teflon® stirrer bearing,septum, and reflux condenser with gas inlet while purging with nitrogen.Anhydrous THF (1 L) was transferred to the flask by cannula and stirredto partially disperse the pulp. Inside the glove box, a 1M solution ofP₄tBu in hexane (13 mL, 10 mole %) was added to anhydrous THF (1 L),which was then added by cannula to the Morton flask to give an orangecolor. The mixture was heated to a mild reflux during which the colorintensified to a darker orange. After stirring for about 4 hours, theorange pulp was finely dispersed in the solution and the mixture wascooled to room temperature. Inside the glove box, 4,4’-methylenebis(N,N-diglycidylaniline) (11 g, 26 millimoles) was dissolved inanhydrous THF (100 mL), which was then added by cannula to the Mortonflask. The pulp became yellow-orange color as it was stirred overnight.The mixture was quenched with methanol (200 mL) then vacuum filtered tocollect the yellow pulp. The pulp was washed three times with methanol(1400 mL) then three times with deionized water (1400 mL). A portion ofthe wet pulp was dried under high vacuum to determine percent solids of24.1%. TGA showed a weight loss of 4.1 wt % between 200 and 500° C. dueto the grafted epoxy groups. ATR IR showed a decrease in the absorbanceat 3300 cm⁻¹ for amide NH groups relative to untreated pulp.

Example 40

Freeze-dried Kevlar® pulp (16 g, 130 millimoles amide groups) with aspecific surface area of 16.8 m²/g was placed in a 3 L three-neck Mortonflask and dried at 120° C. in a vacuum oven. The flask was equipped witha stainless steel stirring rod, gas-tight Teflon® stirrer bearing,septum, and reflux condenser with gas inlet while purging with nitrogen.Anhydrous THF (1 L) was transferred to the flask by cannula and stirredto partially disperse the pulp. Inside the glove box, a 1M solution ofP₄tBu in hexane (6.5 mL, 5 mole %) was added to anhydrous THF (1 L),which was then added by cannula to the Morton flask to give anorange-colored pulp. The mixture was heated to a mild reflux. Afterstirring for about 4 hours, the orange pulp was finely dispersed in thesolution and the mixture was cooled to room temperature. Inside theglove box, N-(4-vinylphenyl)maleimide (2.6 g, 13 millimoles) wasdissolved in anhydrous THF (100 mL), which was then added by cannula tothe Morton flask. The pulp became yellow-orange color as it was stirredovernight. The mixture was quenched with methanol (200 mL) then vacuumfiltered to collect the yellow pulp. The pulp was washed three timeswith methanol (1400 mL) then three times with deionized water (1400 mL).A portion of the wet pulp was dried under high vacuum to determinepercent solids of 26.4%. TGA showed a weight loss of 2.7 wt % between200 and 475° C. due to the grafted polymerization of the maleimidegroups. ATR IR showed an absorbance at 1707 cm⁻¹ for the grafted imidecarbonyl groups.

Comparative Example J

Kevlar® pulp 1F361 (40 g, 50% solids) was dispersed in water (1000 g)using a laboratory blender to give a homogeneous slurry. Alcogum® 6940(10 g, 11% solids), Alcogum® SL 70 (2.2 g, 15% solids), Aquamix® 549(4.1 g, 15% solids), and Aquamix® 125 (4.3 g, 14.5% solids) were addedto the blender and dispersed into the slurry. Natural rubber latex (108g, 62% solids) was added to the blender and dispersed into the slurry.The slurry was poured into an open container and the blender jar wasrinsed with water to collect all of the slurry. The latex was coagulatedby adding an aqueous solution containing calcium chloride (26 wt %) andacetic acid (5.2 wt %) with gentle stirring until the pH was between 5.8and 5.2. The coagulated mass was collected and pressed to remove as muchof the aqueous phase as possible. The mass was then dried overnight at70° C. in a vacuum oven under nitrogen purge to give a natural rubbermasterbatch containing 23% pulp.

A rubber compound containing 5 phr pulp was prepared by adding thefollowing materials to a C. W. Brabender Prep-Mixer® equipped with cammixing blades: natural rubber (192.5 g), the masterbatch (50.25 g),stearic acid (6.94 g, 3 phr), zinc oxide (6.94 g, 3 phr), rubbermaker'ssulfur (3.70 g, 1.6 phr), Amax® OBTS (1.85 g, 0.8 phr), DPG (0.92 g, 0.4phr), Santoflex® 6PPD (4.62 g, 2 phr), and AgeRite® Resin D (2.31 g, 1phr). The compound was mixed at 80-95° C. for 25-30 minutes at 75-100rpm, then removed from the mixing chamber and blades. The compound wasmixed firther and homogenized using an EEMCO 2 roll laboratory mill with6 inch by 12 inch wide rolls. The final compound was sheeted to athickness of 2.0-2.2 mm. Two 4 inch by 6 inch plaques were cut from themilled sheet in the machine direction, and another two plaques were cutin the cross-machine direction. The plaques were compression molded at160° C. to cure the natural rubber.

Dumbell tensile bars were cut from the cured plaques. The tensileproperties are shown in Table 6.

Example 41

The procedure of Comparative Example J was modified to prepare a naturalrubber masterbatch containing 22% of the MBDGA-grafted pulp of Example22 (15 g) and 37% of vinylpyridine terpolymer by adjusting the requiredquantities of the other materials and adding GenTac® FS vinylpyridinelatex (61 g, 41% solids) before the other additives and the naturalrubber latex. The rubber compound was then made and tested as describedin Comparative Example J. The tensile properties are shown in Table 6.

TABLE 6 Example 41 J Test Direction MD XD MD XD Stress, 10% Strain (MPa)0.90 0.72 0.83 0.70 Stress, 25% Strain (MPa) 2.51 1.62 2.06 1.64 Stress,50% Strain (MPa) 4.74 2.67 3.91 2.86 Stress, 100% Strain (MPa) 5.45 3.675.14 3.99 Stress, 200% Strain (MPa) 6.15 4.80 6.11 5.14 Stress, 300%Strain (MPa) 7.60 6.37 7.89 6.72 Strain at Break, % 306 395 392 475

What is claimed is:
 1. A fiber comprising poly(p-phenyleneterephthalamide) having N-(4-vinylphenyl)maleimide groups grafted ontothe fiber surface.
 2. The fiber of claim 1 wherein theN-(4-vinylphenyl)maleimide groups have undergone graft polymerizationonto the fiber surface.
 3. The fiber of claim 1 wherein theN-(4-vinylphenyl)maleimide groups comprise 0.1 to 10 weight % of thetotal weight of the fiber.
 4. The fiber of claim 1 wherein the hydrogenon 0.25 to 75 mole percent of the amide sites of the poly(p-phenyleneterephthalamide) on the fiber surface have been replaced by graftingN-(4-vinylphenyl)maleimide groups.
 5. The fiber of claim 3 wherein theN-(4-vinylphenyl)maleimide groups comprise 1 to 10 weight % of the totalweight of the fiber.
 6. The fiber of claim 4 wherein the hydrogen on 10to 50 mole percent of the amide sites on the fiber surface have beenreplaced by grafting N-(4-vinylphenyl)maleimide groups.
 7. A continuousfilament yarn, cord, spun staple yarn, nonwoven fabric, floc, pulp orchopped strand comprising the fiber of claim
 1. 8. A fiber-reinforcedcomposite comprising a matrix resin and a continuous filament yarn, spunstaple yarn, nonwoven fabric, floc, pulp or chopped strand of claim 7.9. A fiber-reinforced rubber article comprising an elastomer and acontinuous filament yarn, cord, spun staple yarn, nonwoven fabric, floc,pulp or chopped strand of claim
 7. 10. A dipped cord suitable for use ina rubber compound comprising the fiber of claim 1 coated with astyrene-butadiene-vinylpyridine rubber latex.